High-peak-power pulsed lasers that operate at high repetition rates enable optical parametric chirped-pulse amplification (OPCPA) for high-harmonic generation (HHG). This HHG can be used for tabletop generation of coherent x-rays, generating seeds for free-electron lasers, high-brightness photo-injection for advanced accelerators, and laser-wakefield acceleration. They can also enable industrial applications including but not limited to laser peening for strengthening metal parts, percussion drilling of deep holes in super-alloys used in turbine blades, and forming aerodynamic surfaces from thick metal sections used for wings in the aerospace industry and many other industrial applications.
In HHG, an intense laser beam, such as a pulse train emitted by an OPCPA, illuminates an atomic medium, which emits all of its odd harmonics of the laser frequency (up to some cutoff order) in the forward direction. These harmonics, which have comparable efficiency, may be used for high-harmonic spectroscopy and for photolithography. HHG driven by long wavelengths (e.g., about 2-5 μm) extends the high harmonics' cutoff order to the water-window and even to the keV regions of the electromagnetic spectrum thanks in part to pump laser technology based on optical parametric amplification (OPA) and OPCPA. (As understood by those of skill in the art, the water window is a band of the electromagnetic spectrum that stretches from the K-absorption edge of oxygen at a wavelength of about 2.34 nm (530 eV) to the K-absorption edge of carbon at about 4.4 nm (280 eV). Water is relatively transparent to radiation in this band.)
Phase-matched HHG at high photon energies has been experimentally demonstrated using a 10 Hz, multi-millijoule, 1.5 μm to 2 μm OPA source and a 20 Hz, multi-millijoule, 3.9 μm OPCPA source. The number of the soft X-ray photons generated per second over 1% bandwidth, however, is still as low as 106 to 107, limiting the usefulness of the existing OPA and OPCPA sources.
Laser wakefield acceleration involves using high-intensity laser pulses to generate a plasma for accelerating electrons. Illuminating the plasma with a laser pulse creates a wave that propagates through the plasma at a speed near light speed. As this wave propagates, it displaces background electrons through the ponderomotive force (or light pressure) of the laser. For large enough plasma waves, electrons in the background plasma can be trapped and accelerated by the waves' longitudinal electric fields to very high energies over very short distances. The accelerated electrons can be used to form an energetic electron beam suitable for radiography, radioisotope production, nuclear physics, and possibly the transmutation of nuclear waste
Laser peening, or laser shock peening, is a process for hardening or peening metal that involves using short pulses of laser light to improve the fatigue resistance of a piece of metal, such as a turbine blade in a jet engine. Focusing the pulses on an ablative coating, such as absorptive paint or tape, on the metal's surface causes the coating to explode, which produces a shock wave that compresses the metal. At high enough irradiances (e.g., 10 GW/cm2), the pulses create pressures that plastically yield metal surfaces, leaving deep levels of compressive stress or desired plastic strain in the metal. This deep compressive stress improves the metal's fatigue resistance.